Solid electrolyte high energy battery

ABSTRACT

The present invention is directed to a battery including a solid ionically conductive polymer electrolyte having a first surface and a second surface; a first electrode disposed on the first surface of the solid ionically conductive polymer electrolyte; a second electrode disposed on the second surface of the solid ionically conductive polymer electrolyte; and at least a first conductive terminal and a second conductive terminal, each terminal being in electrical contact with respectively the first conductive electrode and the second conductive electrode. The invention is also directed to a material including a polymer; a dopant; and at least one compound including an ion source; wherein a liberation of a plurality of ions from the ion source provides a conduction mechanism to form an ionically conductive polymer material. The present invention is further directed to methods for making such batteries and materials.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not applicable)

BACKGROUND OF THE INVENTION

Lithium ion (and other) batteries generally employ a liquid electrolytewhich is hazardous to humans and to the environment and which can besubject to fire or explosion. Liquid electrolyte batteries arehermetically sealed in a steel or other strong packaging material whichadds to the weight and bulk of the packaged battery. A new innovation isthe pouch cell, which has been used in lightweight batteries, but thesehave not seen widespread acceptance.

Conventional liquid electrolyte also suffers from the build-up of asolid interface layer at the electrode/electrolyte interface whichcauses eventual failure of the battery. Conventional lithium ionbatteries can also exhibit slow charge times on the order of hours. Inaddition, the batteries suffer from a limited number of recharges sincethe chemical reaction within the battery reaches completion and limitsthe re-chargeability because of corrosion and dendrite formation. Theliquid electrolyte also limits the maximum energy density. Theelectrolyte starts to break down at about 4.2 volts. New industryrequirements for battery power are often 4.8 volts and higher whichcannot be achieved by present liquid electrolyte lithium ion cells.There have been developments in both spinel structures and layered oxidestructures which have not been deployed due to the limitations of theliquid electrolyte. Also, lithium ion batteries with liquid electrolytessuffer from safety problems with respect to flammability of the liquidelectrolyte.

In a conventional lithium ion battery having a liquid electrolyte thereis also a need for a separator in the liquid electrolyte. The separatoris a porous structure which allows for ions to flow through it, andblocks electrons from passing through it. The liquid electrolyte batteryusually requires a vent to relieve pressure in the housing, and inaddition, such conventional batteries usually include safety circuitryto minimize potentially dangerous over-currents and over-temperatures.FIGS. 1 and 2 show schematics and general reactions in such conventionallithium ion batteries.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, a lithium ion battery is providedwhich has a solid polymer electrolyte. The solid electrolyte enables alighter weight and much safer architecture by eliminating the need forheavy and bulky metal hermetic packaging and protection circuitry. Thenovel solid polymer battery can be of smaller size, lighter weight andhigher energy density than liquid electrolyte batteries of the samecapacity. The solid polymer battery also benefits from less complexmanufacturing processes, lower cost and reduced safety hazard, as theelectrolyte material is non-flammable. The novel battery will alsoprovide cell voltages greater than 4.2 volts. The solid electrolyte canbe formed into various shapes by extrusion (and co-extrusion), moldingand other techniques such that different form factors can be providedfor the battery. Particular shapes can be made to fit into differentlyshaped enclosures in devices or equipment being powered. In addition,the novel battery does not require a separator, as with liquidelectrolyte batteries, between the electrolyte and electrodes, nor doesthe novel battery require a vent. The weight of the novel battery issubstantially less than a battery of conventional construction havingsimilar power capacity. In some embodiments, the weight of the novelbattery can be less than half the weight of a conventional battery.

The electrolyte material is a solid ionically conductive polymer whichhas preferably a semi-crystalline or crystalline structure whichprovides a high density of sites for ionic transport. The polymerstructure can be folded back on itself. This will allow for new batteryformats.

According to one aspect of the invention, the electrolyte is in the formof an ionic polymer film. An electrode material is directly applied toeach surface of the electrolyte and a foil charge collector or terminalis applied over each electrode surface. A light weight protectivepolymer covering can be applied over the terminals to complete the filmbased structure. This thin film battery is flexible and can be rolled orfolded into intended shapes to suit installation requirements.

According to another aspect of the invention, the electrolyte is in theform of an ionic polymer monofilament (hollow). Electrode materials andcharge collectors are directly applied (co-extruded) to each surface ofthe electrolyte and a terminal is applied at each electrode surface. Alight weight protective polymer covering can be applied over theterminals to complete the structure. This form of battery is thin,flexible, and can be coiled into intended shapes to suit installationrequirements, including very small applications.

According to another aspect of the invention, a solid electrolyte can bemolded in a desired shape. Anode and cathode electrode materials aredisposed on respective opposite surfaces of the electrolyte to form acell unit. Electrical terminals are provided on the anode and cathodeelectrodes of each cell unit for interconnection with other cell unitsto provide a multi cell battery or for connection to a utilizationdevice.

In yet other aspects of the invention, methods for making such batteriesare disclosed.

In all of the above aspects of the invention, the electrode materials(cathode and anode) can be combined with a form of the novel electrolytematerial to further facilitate ionic movement between the twoelectrodes. This is analogous to a conventional liquid electrolytesoaked into each electrode material in a conventional lithium-ionbattery.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following description of theinvention, is better understood when read in conjunction with theappended drawings. For the purpose of illustrating the invention,exemplary constructions are shown in the drawings. The invention is notlimited, however, to the specific methods and instrumentalitiesdisclosed herein.

FIG. 1 shows show a schematic of a conventional lithium ion batteryaccording to the prior art.

FIG. 2 shows reactions at electrodes in a conventional lithium ionbattery according to the prior art.

FIG. 3 exemplarily illustrates a method of the invention including stepsfor manufacturing a solid state battery using an extruded polymer.

FIG. 4 exemplarily illustrates the extrusion process according to theinvention.

FIG. 5 exemplarily illustrates a schematic representation of anembodiment according to the invention.

FIG. 6 shows a schematic of a solid polymer battery with polyethyleneoxide according to the prior art.

FIG. 7 shows a dynamic scanning calorimetry plot showing the glasstransition temperature and melting temperature of polyethylene oxideaccording to prior art.

FIG. 8 shows the relationship of ionic conductivity versus temperatureof traditional amorphous polyethylene oxide according to the prior art.

FIG. 9 shows a schematic illustration of amorphous and crystallinepolymers.

FIG. 10 exemplarily shows a resulting formula for the crystallinepolymer of the present invention.

FIG. 11 exemplarily illustrates a dynamic scanning calorimeter curve ofa semicrystalline polymer.

FIG. 12 exemplarily illustrates formulations which were investigated foruse with the invention.

FIG. 13 exemplarily illustrates a chemical diagram of2,3-dicyano-5,6-dichlorodicyanoquinone (DDQ).

FIG. 14 exemplarily illustrates possible mechanisms of conduction of thesolid electrolyte polymer according to the invention.

FIG. 15 exemplarily illustrates a plot of the conductivity of theionically conductive polymer according to the invention in comparisonwith a liquid electrolyte and a polyethylene oxide lithium saltcompound.

FIG. 16 exemplarily illustrates the mechanical properties of theionically conducting film according to the invention.

FIG. 17 exemplarily shows a UL94 flammability test conducted on apolymer according to the invention.

FIG. 18 exemplarily shows a plot of volts versus current of an ionicallyconductive polymer according to the invention versus lithium metal.

FIG. 19 exemplarily illustrates a schematic of extruded ionicallyconductive electrolyte and electrode components according to theinvention.

FIG. 20 exemplarily illustrates the solid state battery according to theinvention where electrode and electrolyte are bonded together.

FIG. 21 exemplarily illustrates a final solid state battery according tothe invention having a new and flexible form.

DETAILED DESCRIPTION OF THE INVENTION

The inventor has developed a non-flammable solid polymer electrolytewhich is conductive at room temperature and can be used in any batteryapplication. The material's novel conductivity mechanism improves energydensity by 10-fold and reduces battery costs by up to 50%.

Existing solid state polymers used for ionic conductivity are based onalkali metals blended with polyethylene oxide (PEO). The three primarylimitations with PEO are its temperature limitations, safety issues incommercial applications, and its manufacturability.

The limited temperature range of PEO. PEO according to the prior art isconductive only above the material's glass transition temperature(typically >50° C.); below that temperature it is in a glassy state andlacks conductivity. Above that temperature PEO exists in a visco-elasticstate through which ions can conduct via chain mobility. Accordingly,the current blends of PEO with other materials used in laboratory andcommercial applications all require high temperatures (>50° C.) toachieve the state necessary for the polymer to be reactive. This hightemperature limits the kinds of applications PEO can be used in, evenwith necessary safety precautions for thermal runaway.

The flammability of PEO. PEOs according to the prior art are flammable,due to their volatile nature and high operating temperature. Currently,a battery utilizing PEO as an electrolyte requires a hermetic packagearound it to prevent thermal runaway. This adds an expensive thermalmanagement system, adds safety risk to the end user, which can preventend user adoption, and creates a rigid, bulky structure which thebattery management system has to be designed around.

Manufacturability of PEO batteries. Commercial PEO manufacturerscurrently spray the polymer onto the electrodes during manufacturing.This batch-scale process is inefficient, and creates an end product thatis stiff, thick, and costly to integrate into an end application.Moreover, although PEO has been in existence for over 20 years, it isstill not commercially produced.

Liquid electrolytes embody many of the same problems as PEO as used inthe prior art: high cost, safety concerns, cost and manufacturabilitychallenges, poor mechanical properties and often a cause of performancedegradation. The solid polymer approach of the present invention solvesthe problems associated with liquid electrolytes and addresses thelimitations of PEO material.

The invention offers three key advantages in its polymer performancecharacteristics: (1) It has an expansive temperature range. In lab-scaletesting, the crystalline polymer design has shown high ionicconductivity both at room temperature and over a wide temperature range.(2) It is non-flammable. The polymer self-extinguishes, passing theUL-V0 Flammability Test. The ability to operate at room temperature andthe non-flammable characteristics demonstrate a transformative safetyimprovement that eliminates expensive thermal management systems. (3) Itoffers low-cost bulk manufacturing. Rather than spraying the polymeronto electrodes, the polymer material can be extruded into a thin filmvia a roll-to-roll process, an industry standard for plasticsmanufacturers. After the film is extruded, it can be coated with theelectrode and charge collector materials to build a battery “from theinside out.” This enables thin, flexible form factors without the needfor hermetic packaging, resulting in easy integration into vehicle andstorage applications at low cost.

The solid polymer electrolyte of the present invention is based on atransformative material that creates a new ionic conduction mechanismthat provides a higher density of sites for ionic transport and allowshigher voltages to run through the electrolyte with no risk of thermalrunaway or damage to ion transport sites from lithiation. Thischaracteristic enables a durable electrolyte for higher voltage cathodeand anode materials in thin-film applications, resulting in higherenergy densities for batteries in vehicle and stationary storageapplications. The ability to run high voltages through an electrolytethat is conductive, mechanically robust, chemical and moistureresistant, and nonflammable not only at room temperature, but over awide range of temperatures, will allow integration of high performanceelectrodes without costly thermal and safety mechanisms employed by theindustry today.

Batteries prepared using the polymer electrolyte of the presentinvention are characterized by a 10-fold energy density improvement overcurrent commercially available electrolytes, as well as a performancerange of −40° C. to 150° C. with minimal conductivity degradation. Thepolymer electrolyte can be extruded by a process that produces workingpolymers at a thickness of 6 microns, which enables these traits in athin-film format under commercial manufacturing conditions at batchscale. The polymer electrolyte allows the development of new, highthroughput, low-cost manufacturing lines for solid electrolyteproduction, and can be integrated into a variety of product lines,including lithium and zinc battery manufacture. In addition, the polymerelectrolyte is not limited to use in batteries, but can be used in anydevice or composition that includes an electrolyte material. Forexample, the polymer electrolyte material can be used in chemicalseparation processes, such as for the separation of ions, inelectrochromic devices, electrochemical sensors, and fuel cellmembranes.

FIG. 3 shows a method of manufacturing a solid state battery using anextruded polymer according to the invention. The material is compoundedinto pellets, and then extruded through a die to make films of variablethicknesses. The electrodes can be applied to the film using severaltechniques, such as sputtering or conventional casting in a slurry.

FIG. 4 shows a method of manufacturing of an ionic polymer filmaccording to the invention, which involves heating the film to atemperature around 295° C., and then casting the film onto a chill rollwhich freezes the plastic. The film can be very thin, in the range of 10microns thick or less. FIG. 5 shows a schematic representation of thearchitecture of an embodiment according to the invention.

Previous attempts to fabricate polymer electrolytes were based on aspecific ionically conductive material whose mechanism was discovered in1973. The material is polyethylene oxide(PEO), and the ionic conductionmechanism is based on the “chain mobility” concept, which requires thepolymer to be at a temperature higher than the glass transitiontemperature. FIG. 6 shows a schematic of a solid polymer battery withpolyethylene oxide according to the prior art. Included in FIG. 7 is adynamic scanning calorimetry (DSC) plot showing the glass transitiontemperature (T_(g)) and the melting temperature (T_(m)) of PEO.

The mechanism for ion transport involves “motion” of the amorphouschains above the T_(g). Above this temperature the polymer is very“soft” and its mechanical properties are very low. For application inlithium ion batteries, traditional lithium ion salts are used asadditives such as LiPF₆, LiBP₄, or LiCLO₄. Lithium salts are a source ofissues in conventional Li ion batteries such as corrosion, reliability,and high cost. FIG. 8 is a plot which shows the relationship of ionicconductivity versus temperature of traditional amorphous polymer (PEO)according to the prior art. FIG. 8 shows that traditional amorphouspolymer (PEO) does not have meaningful conductivity at room temperature.

The solid polymer electrolyte according to the invention has thefollowing characteristics: ionic conduction mechanism at roomtemperature, wide temperature range, ion “hopping” from a high densityof atomic sites, and a new means of supplying ions (lithium orotherwise)

The invention uses a “crystalline or semi-crystalline polymer”,exemplarily illustrated in FIG. 9, which typically is above acrystallinity value of 30%, and has a glass transition temperature above200° C., and a melting temperature above 250° C. Added to this arecompounds containing appropriate ions which are in stable form which canbe modified after creation of the film. FIG. 10 shows the molecularstructure of the crystalline polymer. The molecular weight of themonomeric unit of the polymer is 108.16 g/mol.

Typical compounds for ion sources include, but are not limited to, Li₂O,LiOH, and ZnO. Other examples are TiO₂, Al₃O₂, and the like.Additionally other additives may be included to further enhanceconductivity or current density, such as carbon nanotubes or the like.After the film is created, a doping procedure can be used, using anelectron acceptor. Alternatively the dopant can be “pre-mixed” with theinitial ingredients and extruded without post processing. The purpose ofthe electron acceptor is two-fold: release ions for transport mobility,and to create polar high density sites within the polymer to allow forionic conductivity. Note: there is a clear distinction betweenelectrical conductivity and ionic conductivity.

Typical materials that can be used for the polymer include liquidcrystal polymers and polyphenylene sulfide (PPS), or any semicrystallinepolymer with a crystallinity index greater than 30%, or other typicaloxygen acceptors. FIG. 11 exemplarily illustrates a dynamic scanningcalorimeter curve of a semicrystalline polymer. Table 1 of FIG. 12illustrates exemplary formulations which were investigated.

Electron acceptors can be supplied in a vapor doping process. They canalso be pre-mixed with the other ingredients. Typical electron acceptorssuitable for use include, but are not limited to:2,3-dicyano-5,6-dichlorodicyanoquinone (DDQ) (C₈Cl₂N₂O₂) as exemplarilyillustrated in FIG. 13, Tetracyanoethylene (TCNE) (C₆N₄), and sulfurtrioxide (SO₃). A preferred dopant is DDQ, and doping is preferablyperformed in the presence of heat and vacuum.

FIG. 14 shows possible mechanisms of conduction of the solid electrolytepolymer according to the invention. Charge carrier complexes are set upin the polymer as a result of the doping process.

Extruded films have been made in thickness ranges from 0.0003″ thick to0.005″. Surface conductivity measurements have been made, and theresults are reported in FIG. 15. In FIG. 15, the conductivity ofionically conductive polymer according to the invention (A) is comparedwith that of trifluoromethane sulfonate PEO (□) and the liquidelectrolyte Celgard/(EC:PC/LiP F6) (◯). The conductivity of the ionicpolymer according to the invention tracks the conductivity of the liquidelectrolyte and far surpasses that of trifluoromethane sulfonate PEO atthe lower temperatures.

FIG. 16 shows the mechanical properties of the ionically conductive filmof the invention which were evaluated using ISPM IPC-TM-650 Test MethodsManual2.4.18.3. In the tensile strength versus elongation curve of FIG.16, the “ductile failure” mode indicates that the material can be veryrobust.

Flammability of the polymer was tested using a UL94 flame test. For apolymer to be rated UL94-V0, it must “self-extinguish” within 10 secondsand ‘not drip”. The electrolyte was tested for this property and it wasdetermined that it self-extinguished with 2 seconds, did not drip, andtherefore easily passed the V-0 rating. FIG. 17 shows pictures of theresult.

In addition to the properties of ionic conductivity, flame resistance,high temperature behavior, and good mechanical properties, it'snecessary that the polymer material not be subject to chemical reactionor attack by lithium metal or other active species of the electrodematerials. The traditional test for attack by polymers by lithium isdone by the use of cyclic voltammetry. This is a test where the polymeris sandwiched between a lithium metal anode and blocking stainless steelelectrode. A voltage is applied and it is swept from a low value (˜2volts) up to a high value greater than 4 volts. The current output ismeasured to determine if there is any significant reaction happeningwith the polymer/lithium metal. High output currents would indicate achemical reaction which is not desirable. FIG. 18 shows the result ofthis study and indicates that this ionically conductive polymer isstable to at least 6 volts. The results showed good high voltagestability.

The solid polymer electrolyte according to the invention is able toachieve the following properties: A) high ionic conductivity at roomtemperature and through a wide temperature range (at least −10° C. to+60° C.); B) non-flammability; C) extrudability into thin films allowingfor reel-reel processing and a new way of manufacturing; D)compatibility with Lithium metal and other active materials, thisinvention will allow for the fabrication of a true solid state battery.The invention allows for a new generation of batteries having thefollowing properties:

-   -   No safety issues;    -   New form factors;    -   Large increases in energy density; and    -   large improvements in cost of energy storage.

FIGS. 19, 20 and 21 show several elements of the solid state batterywhich are, respectively: A) extruded electrolyte; B) extruded anodes andcathodes; and C) final solid state battery allowing for new form factorsand flexibility.

While the present invention has been described in conjunction withpreferred embodiments, one of ordinary skill, after reading theforegoing specification, will be able to effect various changes,substitutions of equivalents, and other alterations to that set forthherein. It is therefore intended that the protection granted by LettersPatent hereon be limited only by the definitions contained in theappended claims and equivalents thereof.

1. A solid state battery comprising: a solid ionically conductivepolymer electrolyte having an ionic conductivity greater than 1×10-4S/cm at room temperature; and formed from a polymer, an electronacceptor, and at least one compound comprising an ion source; whereinthe polymer is polyphenylene sulfide, and wherein the compound compriseslithium.
 2. The solid state battery of claim 1, wherein the electrolytecomprises a first surface and a second surface; a first electrodedisposed on the first surface of the solid ionically conductive polymerelectrolyte; a second electrode disposed on the second surface of thesolid ionically conductive polymer electrolyte; and at least a firstconductive terminal and a second conductive terminal, each terminalbeing in electrical contact with respectively the first electrode andthe second electrode.
 3. The battery of claim 1, wherein the solidionically conductive polymer electrolyte is a thin film.
 4. The batteryof claim 2, wherein each of the first and the second electrodes are athin film disposed respectively on the first surface and second surfaceof the solid ionically conductive polymer electrolyte.
 5. The battery ofclaim 2, wherein at least one of the first and the second electrodes isextruded.
 6. The battery of claim 1, wherein the solid ionicallyconductive polymer electrolyte is extruded.
 7. The battery of claim 1,wherein the solid ionically conductive polymer electrolyte has acrystallinity index greater than at least 30%.
 8. The battery of claim2, wherein the first electrode is an anode and comprises the solidionically conductive polymer electrolyte and a first electrochemicallyactive material.
 9. The battery of claim 2, wherein the second electrodeis a cathode and comprises the solid ionically conductive polymerelectrolyte and a second electrochemically active material.
 10. Thebattery of claim 2, wherein the electrolyte and at least one electrodeis co-extruded.